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Get a Service by Service Type and Name

You can also request a named configuration for a given service type by using the overloads of IContainer.GetInstance() that take in a name like this:

cs
[Fact]
public void get_a_named_instance()
{
    var container = new Container(x =>
    {
        x.For<IWidget>().Add<AWidget>().Named("A");
        x.For<IWidget>().Add<BWidget>().Named("B");
        x.For<IWidget>().Add<CWidget>().Named("C");
    });

    container.GetInstance<IWidget>("A").ShouldBeOfType<AWidget>();
    container.GetInstance<IWidget>("B").ShouldBeOfType<BWidget>();
    container.GetInstance<IWidget>("C").ShouldBeOfType<CWidget>();

    // or

    container.GetInstance(typeof(IWidget), "A").ShouldBeOfType<AWidget>();
    container.GetInstance(typeof(IWidget), "B").ShouldBeOfType<BWidget>();
    container.GetInstance(typeof(IWidget), "C").ShouldBeOfType<CWidget>();
}

snippet source | anchor

cs
[Fact]
public void get_a_named_instance()
{
    var container = new Container(x =>
    {
        x.For<IWidget>().Add<AWidget>().Named("A");
        x.For<IWidget>().Add<BWidget>().Named("B");
        x.For<IWidget>().Add<CWidget>().Named("C");
    });

    container.GetInstance<IWidget>("A").ShouldBeOfType<AWidget>();
    container.GetInstance<IWidget>("B").ShouldBeOfType<BWidget>();
    container.GetInstance<IWidget>("C").ShouldBeOfType<CWidget>();

    // or

    container.GetInstance(typeof(IWidget), "A").ShouldBeOfType<AWidget>();
    container.GetInstance(typeof(IWidget), "B").ShouldBeOfType<BWidget>();
    container.GetInstance(typeof(IWidget), "C").ShouldBeOfType<CWidget>();
}

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.NET Core Keyed Services

While Lamar (and StructureMap before that) has supported the idea of named service registrations in production applications since 2004 (!), .NET finally discovered this usage in .NET 8. Lamar 12.1.0 introduces native support for keyed services according to the new .NET standard as shown below:

cs
[Fact]
public void register_by_name_using_dot_net_core_syntax()
{
    var container = Container.For(services =>
    {
        
        services.AddKeyedSingleton<IWidget, AWidget>("one");
        services.AddKeyedScoped<IWidget>("two", (_, _) => new BWidget());
        services.AddKeyedSingleton<IWidget>("three", new CWidget());

        services.AddKeyedSingleton<CWidget>("C1");
        services.AddKeyedSingleton<CWidget>("C2");
        services.AddKeyedSingleton<CWidget>("C3");
    });

    container.GetInstance<IWidget>("one").ShouldBeOfType<AWidget>();
    container.GetKeyedService<IWidget>("one").ShouldBeOfType<AWidget>();
    
    container.GetInstance<IWidget>("two").ShouldBeOfType<BWidget>();
    container.GetKeyedService<IWidget>("two").ShouldBeOfType<BWidget>();
    
    container.GetInstance<IWidget>("three").ShouldBeOfType<CWidget>();
    container.GetKeyedService<IWidget>("three").ShouldBeOfType<CWidget>();
    
    container.GetInstance<CWidget>("C1").ShouldBeOfType<CWidget>();
    container.GetKeyedService<CWidget>("C2").ShouldBeOfType<CWidget>();
    
    container.GetKeyedService<CWidget>("C2")
        .ShouldBeSameAs(container.GetKeyedService<CWidget>("C2"));
    
    container.GetKeyedService<CWidget>("C2")
        .ShouldNotBeSameAs(container.GetKeyedService<CWidget>("C3"));
}

snippet source | anchor